Synonyms and related words :
adverse, analytic, annoying, antagonistic, arduous, backbreaking, besetting, bothersome, burdensome, conflicting, contrary, counter, counteractive, crushing, cut-and-try, demanding, detrimental, devitalizing, difficult, dispiriting, disquieting, distressing, draining, empirical, enervating, enfeebling, exacting, examinational, examinatorial, examining, exasperating, exhausting, exigent, experimental, explorational, explorative, exploratory, fact-finding, fatiguesome, fatiguing, feeling, frustrating, groping, grueling, hard, harmful, heavy, hefty, heuristic, hit-or-miss, hostile, in opposition, indagative, infuriating, inimical, inspectional, inspectorial, investigational, investigative, investigatory, irksome, irritating, killing, maddening, miserable, not easy, onerous, opposed, opposing, opposite, oppressive, painful, pilot, plaguey, probationary, probative, probatory, proving, provisional, punishing, rigorous, rough, sapping, sinister, sticky, straining, strenuous, stressful, superincumbent, taxing, tentative, test, testing, tiresome, tiring, toilsome, tough, trial, trial-and-error, tricksy, tricky, troublesome, troublous, unfavorable, untoward, upsetting, verificatory, vexatious, vexing, weakening, weariful, wearing, wearisome, wearying, weighty, worrisome, worrying, wretched, zetetic